In this wireless world, why does a connected factory come with a big helping of spaghetti?

I'm a radio engineer.

Wires are old-fashioned and have no place in the connected factory, right? Industry 4.0 brings the most modern practices: simple installation, no messy umbilicals, empty cable ducts and touch screen control from your phone.

Erm . . . no.

I'd happily connect modern plant with ethernet. But Wifi? No way. How about Zigbee or Z-Wave? Perhaps 2G, 3G, 4G, 5G, NBIoT or LTE? Bluetooth or Wireless Hart? The simple truth is: None of these nor the other standards will displace the need for cables.

There are plenty of positive reasons to go wireless, so why do wires persist? I hear you cry. Here are couple of reasons why cables are here to stay:

PowerTo provide (electric) power, I still must use wires anyway. Having control wiring as well is not an issue if it is provided alongside the power, or better still, if it shares the power connection (such as Power Over Ethernet). Besides, changing batteries is expensive and adding to an inevitable environmental disaster.

Safety & ReliabilityRadio is a shared medium (1). No matter how clever the radio standard, whether you use private frequencies and even if you keep well away from the open bands used by WiFi et al - something will interfere with it eventually. The only thing guaranteed is that you will lose data over a radio ink. Equipment manufacturers go to great lengths to get around this issue by using handshaking, redundancy, multiple transmissions, frequency hopping and spread spectrum.All of the above methods improve the reliability; however, it also increases the latency. And it is still not 100% reliable. I’m afraid the factory is an (electromagnetically) noisy environment.

SecurityRadio is a shared medium (2). It is open to interception, spoofing and jamming. Therefore, encryption is essential. However, this still relies on end-to-end security of the system: device authentication, key handling, correct protocol implementations and of course, the most insecure part of the system - the user. Wires or fibre require physical interception and therefore are inherently more secure.

Performance & SpeedThere is only so much bandwidth available in radio. Need a higher data rate for a cable? Just stick in a 10Gb ethernet link. Want guaranteed access and no contention? Add another cable. Simple.

CostIn economic terms, you ought to use a lot of cable to justify a radio link when it comes to cost savings. Moreover, installation of radio is not free. It can become a highly technical installation, ensuring that there is good signal strength and that the device joins and stays on the correct network. This is how radio engineers justify their massive salary (I do hope the boss is reading this). Then factor in the in-life costs like battery changes, servicing, replacing damaged antennas – it all adds up.

SimplicityYes, there's even a place for KISS in the factory. Keep It Simple, Stupid. A wire is easy to trace, it's function is well defined and can be connected with the most basic of tools and only a elementary understanding.

In summary, wireless is great for bolt-ons, as a monitoring and control system for non-critical applications. But the cable is still king.